Oscillator circuits



April 30, 1935. DE WlTT R. GODDARD 1,999,655

OSCILLATOR CIRCUITS Filed March 14, 1932 our/ 01 INVENTORI DE R. GODDARD ATTORNEY Patented A r. 30, i935 Radio Corporation of America,

Delaware a corporation of r Application March 14, 1932 Serial No. 598,567 4 Glaims. (Cl. 25036) Heretofore in oscillators whose frequency of operation has been] controlled by a resonant system such as a piezo-electric crystal, it has been customary to use separate crystal units vconsisting say of a. crystal, tube and heater for changeover frombne frequency of operation to another. Therefore, change of wave length required switching from one of the units formed of the crystal, heater and the. like, to another.

It is the objectof my present invention to provide a system wherein changeover may be accomplished more simply and cheaply and, in general, by change in voltage applied to a single tube with which there are associated a plurality of resonant systems preferably in the form of piezoelectric crystals.

My present invention is described more fully with the aid of the accompanying drawing wherein,

Figure l is a wiring diagram of my present invention illustrating the manner in which frequency changeover from one piezo-electric crystal to another may be accomplished by varying either the plate voltage or screen grid voltage or both of an electron discharge device, and,

Figure 2 illustrates a complete transmitter wherein changeover from one crystal frequency to another may be accomplished by variation in plate voltage of the electron discharge device forming the master control oscillator.

Referring to Figure 1 I have illustrated a tetrode or screen grid vacuum tube 2 having an electron emitting cathode 4, a control grid 6, a screen grid 8, and an anode or plate It. The voltage to the screen grid is supplied through potentiometer l2 and variable tap l4, and, the voltage to the plate is also supplied from the potentiometer I2 to variable tap l6. Taps l4 and. I6, of course,,permit adjustment of the voltages applied to the plate and screen grid individually.

Between the control grid 6 and the cathode there is inserted a biasing resistor 18. Between the control grid 6 and screen grid 8 there is connected as illustrated a piezo-electric crystal B. In series with crystal B there is another piezoelectric crystal A connected between the control grid 6 and anode ll].

With the circuit as so far described, I have discovered that it is possible to have either crystal oscillate by changing the relative voltages on the plate and screen grid. With the potentiometer delivering a maximum voltage to the anode or plate, crystal A will be found to be the frequency determining element as a result of which output energy of a frequency determined by crystal A may be derived from, for example, the resistor in. the plate supply lead. f

This system then operates with the crystal A establishing feed back between the plate it i and Now, to cause oscillation of the system under the control of crystal B, the plate voltage may be reduced by movement of tap l6 and if desiredat the same time the screen grid potential may be increased. The circuit will then be found to operate at the frequency corresponding to the the system shown in Figure 2, may be used. Connection to point 27 will reduce the relative voltage between the plate and screen grid and hence 1 crystal B will control the frequency of oscillations supplied through conductor 26 to the coupling' tube or buffer amplifier 28. On the other hand, connection to point a will cause, by virtue of increased potential to the plate, frequency controlling action by crystal A of oscillations generated by electron discharge device 2. If desired, in the system shown in Figure 2, change from one frequency controlling system or crystal to another may be accomplished by leaving the switch on either point a or band varying the potential applied to the screen grid 8 by varying the voltage applied to the screen grid by movement of screen grid voltage tap l4.

With the system shown in Figure 2, the output of the crystal controlled oscillator is fed to the coupling tube or buffer amplifier 28 which in turn excites a power amplifier 30 coupled to a radiating antenna 32. If desired, of course, frequency multipliers may be inserted between the buffer amplifier 28 and power amplifier 38 whose output may be varied by variation in voltage applied to the screengrid 34 thereof as indicated.

With the arrangement shown in Figure 2 also, code signaling at crystal controlled frequencies may be accomplished by switching from a point a to point I) utilizing one crystal for indicating spaces, and the other for dots. In this event, of course, the two crystals should operate at frequencies relatively close together. Also some form of relay rather than single pole double throw switch may be used for signaling in this way.

Also, the system shown in Figure 2 may be rality of cold electrodes, a plurality of electr omechanically resonant systems, circuits connecting separate resonantsystems between the control electrode and each of said cold electrodes of said electron discharge device, and, means for varying the voltage applied. to one of the cold electrodes of said device whereby oscillations are generated in accordance withthe voltageapplied at a frequency determined by onlyone of said electromechanioally resonant systems. l

2. In apparatus of the character described, an electron discharge device ha-ving'an electron emitting cathode, a control grid, and a plurality of cold electrodes, a pair of electromechanical vibrators serially connected between said cold electrodes, a connection from said control grid to a point intermediate said serially connected vibrators, and, means for varying the voltage on one of said cold electrodes whereby said electron discharge device generates oscillations at a frequency determined by only one of said vibrators.

3. In apparatus of the character described, an electron discharge device having within an evacuated container an electron emitting cathode, a control grid, a screen grid, and an .anode, 'a pair of piezo-electric crystals serially connected, connected between said anode and screen grid, a

connection from a point intermediate said crystals to the control grid of said electron discharge device, and, means for varying the voltage of the anode with respect to the screen grid whereby either one or the other of said piezo-electric crystals determines the frequency of the output of said electron discharge device.

4; In apparatus of the character described, an electron discharge device having an anode a cathode a control grid and a screen grid, apair of piezoelectric crystalsserially-connected, connected between said'anode and screen grid, '8. resistance connected between said control grid-and cathode, a connection-from said control'grid intermediate said piezo-electric-crystals-and, means 'for varying the voltage on said anode whereby either one of said piezo-electric crystals, de-

pendent upon the voltage applied -to saidanode, controls the frequency of oscillations generated by said electron discharge devices.

DE R. GODDARD. 

